linux-kernel - Re: [PATCH 0/1] devpts: use dynamic

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Date:   Thu, 24 Aug 2017 10:54:58 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Stefan Lippers-Hollmann <s.l-h@....de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Thorsten Leemhuis <regressions@...mhuis.info>
Subject: Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name

Stefan Lippers-Hollmann <s.l-h@....de> writes:

> Hi
>
> On 2017-08-23, Eric W. Biederman wrote:
>> Linus Torvalds <torvalds@...ux-foundation.org> writes:
>> > On Wed, Aug 23, 2017 at 6:49 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:  
> [...]
>> This is so far untested (except for compiling) but I think this will
>> work.
>> 
>> I factor out devpts_ptmx_path out of devpts_acquire so the code
>> doesn't have to do unnecessary and confusing work, and add the
>> new function devpts_mnt.
>> 
>> I revert the code to keep anything except a dentry in
>> tty->link->driver_data.
>> 
>> And reduce the peer opening to a single function ptm_open_peer.
>> 
>> It takes lines of code but the result is very straightforward code.
>
> I've given this a quick test, while it seems to fix the initial problem
> with umounting /dev/ptmx, it does introduce a new one - trying to open 
> an xterm (KDE5's konsole to be exact) doesn't open a shell (the shell 
> window remains totally empty) and trying to ssh into the system fails 
> with "PTY allocation request failed on channel 0", logging in via a 
> real tty and creating a new pbuilder chroot from there succeeds.

Weird.  There is at least one leak inducing bug in there.  So perhaps
that is the cause.   *Scratches my head*  Are you also testing the new
ioctl?

I will resend shortly with a version that has no differences in the old
code from v4.12 (other than the refactoring in fs/devpts/inode.c).
Which should make it very hard to have a regression.

Eric